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The extent of oxidation and growth derived oxygen contamination for Al0.05Ga0.95Sb grown by metalorganic chemical vapour deposition (MOCVD) were systematically investigated by X-ray photoelectron spectroscopy (XPS) using a system with high-energy resolution. The Sb3d52/ and O1s peaks are well resolved and the Ga3d peaks are also well resolved. As expected, all samples investigated show oxide layers (Al2O3, Sb2O2 and Ga2O5) on their surfaces. In particular the percentage of aluminium-oxide was very high compared with a small percentage of AlSb. This indicates that the surface aluminium is very reactive to oxygen from the environment. Carbon content on the surface was also very high. Deeper into the layer, the carbon signal was below the detection limit of XPS and secondary ion mass spectroscopy (SIMS) indicating that the carbon was due to atmospheric exposure. The results indicate extremely low carbon content for Al0.05Ga0.95Sb epilayers grown using TMAl, TMGa and TMSb as metalorganic precursors in an MOCVD system.